Dr. Sheppard leaves Fernly Park (Ackroyd's estate) and on the way home bumps into a stranger who asked for directions to Ackroyd's residence. At home he receives a phonne call from Fernly Park saying that Ackroyd was murdered. THe next day, Flora Ackroyd suggests to Dr. Sheppard that they recruit Hercule Poirot, the doctor's new neighbour, to solve the murder. Flora is worried that Ralph Paton will be blamed for the crime since he was spotted at Fernly Park and that footprints matching a pari of shoes owned by Paton were found in the dirt outside Ackroyd's study the night before. Paton, who was in a lot of debt, expected to inherit a large amount of money upon Ackroyd's death. Dr. Sheppard points out that after he left Ackroyd's study at 9:30 pm and before the body was found at 10:30 pm, Major Blunt and Geoffrey Raymond overheard someone speaking to Ackroyd in his study.
WHile the police are convinced that Paton is the murderer, Poirot has his own theory. He fixates on a phone call made to Dr. Sheppard from the King's Abbott train station and on a grandfather chair which was moved into the middle of the study when Ackroyd was discovered. Poirot assembles Mr.s Cecil Ackroyd, Miss Flora Akroyd, Major Blunt and Geoffrey Raymond together and accuses them all of hiding something. Mrs. Cecil Ackroyd and Raymond admit that they owed Ackroyd money and his death resolved them of all debts. It turns out that Parker, Ackroyd's employee, was guilty of nothing more than snooping. He had heard about blackmailing and thought that maybe he could get in on the act and blackmail his boss. It turns out that Flora lied about wishing her uncle good night on the night in questions. She sneaked up to his room to steal money to settle some debts of her own. Ackroyd's housekeeper Miss Russell explaing that Charles Kent, the stranger found on the grounds that night, cannot be the murderer. She met Kent, her illegitimate son, at Ackroyd's summer house that night.
Poirot determines that Ackroyd purchased a Dictaphone the week before the murder and therefore that was what people overheard at 9:30 pm on the night of the murder. He also reveals that Dr. Sheppard had been hiding Ralph Paton by pretending he was a patient in the local insane asylum. Poirot declares that Dr. Sheppard is the murderer. He murdered Ackroyd and then programmed the Dictaphone to go off at 9:30 pm. In the meantime he planted the footprints using Paton's shoes. He hid Paton so that he would look more suspicious. Dr. Sheppard's motive was the fact that he was Mrs. Ferrars' blackmailer.
The Murder of Roger Ackroyd, first published in 1926 courtesy http://www.agathachristie.com/stories/the-murder-of-roger-ackroyd.